Rapid growth of network traffic expedites on-going increase of the line card capacity of routers and transport devices. With development of the optical communications industry, technologies related to optical transceiver module on the client side are also evolving continuously. High-rate, low-cost, low-power-consumption, miniaturized and pluggable optical transceiver modules have gradually become a focus of attention of the industry.
In recent years, manufacturers of various modules have launched 100GE client-side modules consecutively, where most transmitter-side solutions employ four stand-alone TOSA (Transmitter Optical Subassembly, transmitter optical subassembly) devices, and an external optical MUX (multiplexer, multiplexer) device combines light output by the four TOSAs, and the light enters a single-mode fiber for transmission. Objectives of many vendors for next-generation optical modules are to reduce the volume and power consumption of transmitter-side key devices by designing an integrated TOSA, to make modules evolve toward miniaturized CFP2 or even CFP4 packages.
In the process of evolving toward the next-generation smaller packages, if the transmitter side of the module adopts an integrated TOSA design solution, it is necessary to integrate four lasers and MUX devices and even laser drivers into a TOSA. How to couple the light output by the four lasers into the single-mode fiber, that is, how to design an integrated optical 4:1 multiplexer device, becomes a hot topic of research. In the prior art, the optical MUX/DEMUX device may adopt a TFF (Thin Film Filter, thin film filter)-based or PLC (Planar Lightwave Circuit, planar lightwave circuit)-based design solution.
One of the existing MUX device design solutions is based on a Zig-Zag TFF. As shown in FIG. 1A, the light output by a multi-path laser is collimated by a lens, reflected and combined by a filter and a reflector for multiple times, and then coupled into a single-mode fiber. The filter array and the reflector make up an optical multiplexer, that is, the optical MUX.
Another MUX device design solution in the prior art is to implement a PLC-based optical MUX device. As shown in FIG. 1B, the light output by the laser is combined by a PLC array-based waveguide grating and then coupled into the single-mode fiber for transmission.
However, the volume of the optical MUX device shown in FIG. 1A is too large and is not suitable for integration In addition, laser light in different channels in the optical MUX device is reflected for different numbers of times, and travels along significantly different optical paths. Consequently, the laser light output by different channels has significantly different incident optical power and optical field energy distribution. A great insertion loss exists in the coupling between the optical MUX device shown in FIG. 1B and the laser, and a great insertion loss also exists in the coupling between the MUX device and the fiber. To meet the application requirement of the system, the output optical power of the laser needs to be improved to compensate for the insertion loss, which leads to increase of the overall power consumption and deterioration of the system reliability.